I highly recommend keeping these links because they motivate users to register, e.g. a guest user clicks the Add to Favorites link and the login/register popup appears, after the registration user can bookmark a listing. Otherwise logged-out users will not even know that the favorites feature exists, while it can motivate some users to register (e.g. to keep a list of favorite listings).
If you want to hide these anyway, this is possible via the CSS code snippet, for example you can try this one: